I would suspect that this is the measurement of the brake rotor thickness. More than likely it is rotor thickness in millameters. Unfortunately my MB software does not give me Euro model specs so I can't be for sure if this is within spec, but I can tell you that on the US model C230 of this year (which may very well use the same rotor) the min rotor thickness is 22.0mm. This would mean you are over by 1.2mm.